The field of this invention relates to a pump or compressor for producing air or gas under pressure to inflate an object, such as a vehicle tire. More particularly, the invention relates to an electrically driven air compressor preferably powered by the car battery. Compressed air has been produced by use of a hand or foot pump in which the air is pressured by physical strength. Such foot pumps are illustrated in U.S. Pat. No. 1,280,511 to Macbeth, dated Oct. 1, 1918, and U.S. Pat. No. 1,160,528 to Pilkington, dated Nov. 16, 1915, and in British Pat. No. 1,182,102, published Feb. 22, 1970. In these patents, the pressure of the air in the pressurized air line leading to the object is measured by a gauge connected to the air line. Also, as illustrated in U.S. Pat. No. 1,831,379 to Creser, dated Nov. 10, 1931 and British Pat. No. 296,915 accepted Sept. 13, 1928, a relief valve can be connected to the pressurized air line to bleed air from the line to atmosphere when the air reaches a predetermined selected valve.
Small electrically driven air compressors have also been utilized to inflate tires and other objects and can be provided with similar gauges or relief valves in the pressurized air line leading to the object to be inflated. However, since the gauges and relief valves of the prior art are located in the main pressurized air line leading to the inflatable object, these devices are subject to the pressure variations in the pressure line produced by the pump during each stroke and will not be responsive to the pressure in the object which is the important quantity. In pending application Ser. No. 946,665 filed Sept. 28, 1978, by Edwin L. Schwartz and assigned to the same assignee, there is disclosed devices which isolate the relief valve from pressure pulses which exceed the pressure in the inflatable object so that a false relief to atmosphere will not result before the inflatable object has reached the desired inflation pressure.
In previously mentioned U.S. Pat. No. 1,831,379, it is proposed to discharge all of the high pressure air produced by the compressor through a coiled pipe of fine bore in order to smooth out fluctuations in pressure. A standard relief valve is connected with the end of the coil which leads to the main pressure line and to the inflatable object. Therefore, the presssure sensed by the relief valve will always be the same as that in the main pressure line. Thus, the pumping load on the compressor is greatly increased since the complete air volume must pass through the fine bore coil and any pressure surges in the main line will act upon the relief valve.